During the passage from a place characterized from strong brightness to one poorly illuminated, and in the opposite case, correspondent to a fast increase of brightness, in the first moments that succeed the passage it is not possible to have a correct perception of the images; this situation is dangerous when driving a vehicle, as the driver may not be able to distinguish eventual obstacles.
The situation in which the driver interposes darkening lenses (for example sunglasses or dark helmet visors) between his eyes and the external environment is much more dangerous: the fast brightness decrease that is noticeable, for example entering a tunnel, can be so hard to prevent the driver from seeing clearly. The eye, as a matter of fact, also if adapting after some time, perceives a light signal attenuated from the presence of the darkening lenses; such lenses, in fact, continue in filtering the light also when is no longer needed. The driver is then forced to eliminate lenses (take off glasses or lift up visor), dangerous act, specially if done at high speed.
In many sports is necessary to protect eyes with screens suitable for acting as a filter towards solar radiations.
In all that cases it's opportune that the screen is suitable in maintaining a filtering action dependent on the features of intensity and of incident angle of the radiation which is subjected to.
The adjustment of the filtering action is usually done dealing with an appropriate control device: in many sports, and when driving, it's not possible to act with the hands on such control devices as they are involved in carrying out gestures relative to the sporting acts and/or to driving.
It's not possible to convert glasses, helmets' visors or traditional screens, completely transparent (and/or with constant and settled colour or darkening level), into screens with a filtering actions dependent on the incident radiation. Actually are available embodied solutions that approximate the result described above, but they are of poor practical interest because of their slowness in transparency variation and their limits in the filtering action.
This impossibility makes all the currently existing and utilized screens substantially unsuitable for overcoming the previously pointed out problems.